The present technology relates to a solid-state imaging element, a method for manufacturing the solid-state imaging element, and an electronic device, and particularly to a solid-state imaging element having a pixel separating section for separating photoelectric conversion sections from each other for each pixel, a method for manufacturing the solid-state imaging element, and an electronic device using this solid-state imaging element.
When a pixel separating section is formed within a semiconductor layer in which a plurality of photoelectric conversion sections are formed in a solid-state imaging element, ion implantation is performed a plurality of times with implantation energy varied. At this time, the deeper a position in the semiconductor layer, the higher the energy of the ion implantation. Thus, the deeper the position in the semiconductor layer, the wider the spread in a horizontal direction of an impurity being introduced. Thereby, the deeper the position in the semiconductor layer, the wider in the horizontal direction the shape of an impurity region being formed. After the ion implantation, the impurity is diffused by activating annealing, so that the impurity region expands. As a result of the above, the pixel separating section is formed which has a shape that becomes wider in the horizontal direction at a deeper position in the semiconductor layer, and which is further expanded by the diffusion of the impurity. Such a pixel separating section reduces the capacity of the photoelectric conversion sections within the semiconductor layer, thus inviting a decrease in amount of saturation charge (Qs). In a solid-state imaging element having a minute pixel size, in particular, the ratio of such a pixel separating section is increased, and thus such a pixel separating section has a great effect on the decrease in Qs.
Accordingly, in order to miniaturize the pixel separating section, the following method for forming a pixel separating section has been proposed instead of the ion implantation as described above. First, isolating trenches are formed between pixels in a semiconductor substrate from the surface side of the semiconductor substrate. Next, a diffusion part is formed by doping the side walls and bottom parts of the isolating trenches with a dopant (impurity) of a first conductivity type, and then the isolating trenches are backfilled with an isolation material such as silicon oxide, polysilicon, or the like. In addition, a diffusion part (photoelectric conversion section) of a second conductivity type is formed on the surface side of the semiconductor substrate for each pixel. Further, a diffusion part of the first conductivity type is formed from the backside of the semiconductor substrate. Thereafter, a deep thermal drive is applied to bring the diffusion parts of the first conductivity type closer to each other, the diffusion parts of the first conductivity type being formed from the surface side and the backside, respectively, of the semiconductor substrate. Further, contact pads in electric contact with the diffusion part of the first conductivity type and the diffusion part of the second conductivity type, respectively, are thereafter formed on the surface of the semiconductor substrate (see JP-T-2010-536187).